An electric switching device with rotatably journaled movable contacts and two series-connected breaking points per pole is previously known from DE-A-2 845 950. In this switching device the movable contact is attached together with the contact pressure springs in a diametrically through-going hole in a shaft of insulating material. This hole must be sufficiently large to accommodate the spring movement of the contact. For this reason the shaft must have a relatively large diameter, which entails a relatively large mass of the movable system. This is a disadvantage, especially in current-limiting circuit breakers, since the larger movable mass gives lower contact acceleration upon breaking, which reduces the breaking capacity.
In a contact device of a similar kind disclosed in EP-B-0 174 904, in which a double-break movable contact arm has a central bearing arrangement, the movable contact arm exhibits an elongated bearing hole, the longitudinal axis of which is directed perpendicular to the longitudinal axis of the contact arm. This enables the contact arm to be displaced, within certain limits, transversely in the plane of rotation so that approximately the same contact pressure is achieved at the two breaking points, independently of manufacturing tolerances, contact wear, etc. Furthermore, the movable contact arm is formed with stop faces for two catches which constitute parts of a coupling shaft. A drawback with this design is that the movable contact will have large cross-sectional dimensions in the plane of rotation in relation to the dimension perpendicular thereto. This means that the electrodynamic repulsion force, which influences the movable contact arm upon a short circuit, becomes lower than in contact arms which have their main extension perpendicular to the plane of rotation, since the distance between the antiparallel current lines in the contact arms becomes larger. This results in slower contact separation and reduced breaking capacity.